In conclusion, we experimentally demonstrated SNS-TF-QKD with two independent laser sources, in 511 km long haul field-deployed fibers between the city of Jinan and Qingdao. The generated secure key rate is an order higher than the absolute key rate limit of the repeater-less QKD protocol and 3 orders of magnitudes greater than what is expected if the previous QKD field test system over the same length were applied. Our work proves the feasibility of TF-QKD in a practical environment and paves the way towards long haul fiber quantum network. The techniques developed in the work will find immediate applications in more general applications like in quantum repeater [1]}, and phase-based architecture for the quantum internet [2]}.
